Solidifying material for cell electrolyte solution, and cell comprising the solidifying material

ABSTRACT

A solidifying material for a cell electrolyte solution is a block copolymer, which comprises, as segments A, a polymer non-compatible with the cell electrolyte solution and, as segments B, a polymer compatible with the cell electrolyte solution. The solidifying material absorbs and solidifies the cell electrolyte solution. A smallest unit of the block copolymer is A-B-A. To each of the segments B, at least one group selected from the group consisting of a carboxyl group, an ester group, a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonate group and a polyoxyalkylene group is bonded via a -S- bond or a -C- bond.

BACKGROUND OF THE INVENTION

a) Field of the Invention

This invention relates to a solidifying material for cell or battery(hereinafter collectively called “cell”) electrolyte solution and a cellcomprising the solidifying material as a constituent element. The term“cell electrolyte solution” may hereinafter be referred to simply as an“electrolyte solution”, and the term “solidifying material for anelectrolyte solution” may hereinafter be referred to simply as“solidifying material”.

b) Description of the Related Art

As a cell electrolyte is conventionally in a liquid form, it is sealedin a case from the standpoint of safety. To safely hold the electrolytesolution over a long time, the case is required to be strongly built. Asa result, it has heretofore been difficult to form a cell into a thinstructure. It has recently been proposed to have an electrolyte solutionabsorbed in a high molecular substance such that the electrolyte issolidified. This approach is expected not only to avoid leakage of theelectrolyte solution from cells and to provide the cells with improvedsafety but also to achieve higher design tolerances on cellconfigurations, cell thickness reductions, improvements in durability,and higher outputs owing to increases in area.

SUMMARY OF THE INVENTION

The conventional high molecular substances for solidifying electrolytesolutions have crosslinked structures, are insoluble in solvents, and donot melt under heat. Accordingly, they cannot be formed into thin filmsof uniform thickness. Use of a solid electrolyte in the form of a thinfilm is indispensable for the construction of a cell of smallerdimensions, especially of a reduced thickness. Because theabove-described high molecular substances cannot be formed into thinfilms, it has heretofore been difficult to obtain a solid electrolyte inthe form of a thin film of uniform thickness.

An object of the present invention is, therefore, to provide asolidifying material for a cell electrolyte solution, which can beformed into a thin film or sheet (which may hereinafter be collectivelycalled “film”) of uniform thickness and can easily absorb and solidifythe electrolyte solution.

Another object of the present invention is to provide a cell making useof such a solidifying material.

The above-described objects can be achieved by the present invention aswill be described hereinafter.

Described specifically, the present invention, in a first aspectthereof, provides a solidifying material for a cell electrolytesolution, characterized in that the solidifying material is a blockcopolymer comprising, as segments A, a polymer non-compatible with thecell electrolyte solution and, as segments B, a polymer compatible withthe cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution, a smallest unit of the block copolymer is A-B-A,and to each of the segments B, at least one group selected from thegroup consisting of a carboxyl group, an ester group, a hydroxyl group,a sulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded via a —S— bond or a —C— bond; and a cellcomprising the solidifying material as a constituent element.

The present invention, in a second aspect thereof, also provides asolidifying material for a cell electrolyte solution, characterized inthat the solidifying material is a graft copolymer comprising, assegments A, a polymer non-compatible with the cell electrolyte solutionand, as segments B, a polymer compatible with the cell electrolytesolution, and absorbs and solidifies the cell electrolyte solution, andto each of the segments B, at least one group selected from the groupconsisting of a carboxyl group, an ester group, a hydroxyl group, asulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded; and a cell comprising the solidifyingmaterial as a constituent element.

The present invention, in a third aspect thereof, also provides asolidifying material for a cell electrolyte solution, characterized inthat the solidifying material comprises a film or sheet of a polymerhaving properties that the polymer is insoluble in the cell electrolytesolution but the polymer absorbs and solidifies the cell electrolytesolution, and a backing reinforcing the film or sheet, and the backingis a woven fabric, a nonwoven fabric or a porous film; and a cellcomprising the solidifying material as a constituent element.

The solidifying materials according to the present invention can bedissolved or finely dispersed in appropriate solvents or can be causedto melt by heat, so that they can be formed into films each of which hasa desired thickness. Namely, the solidifying materials according to thepresent invention can be formed into thin films of uniform thickness,and can easily absorb and solidify cell electrolyte solutions. As thesefilms can be provided with enhanced strength by reinforcing them withbackings, these films can each be formed with a still reduced thickness.These film-shaped solidifying materials can conveniently absorb andsolidify electrolyte solutions, and the thus-solidified electrolytesolutions have good electrical conductivity and are useful as solidelectrolytes for cells. Upon absorption of electrolyte solution in eachof these films, the volume of the film increases in the direction of itscross-section, in other words, toward an associated electrode, so thatthe contact between the electrode and the film is rendered closer ansurer. Especially when a woven fabric is used as a backing, a reductionin electrical conductivity can be minimized because the woven fabric hasadequate strength despite its large opening area and moreover, asolidifying material having a large particle size can also be used forthe preparation of a coating formulation which is useful for forming afilm.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

(First Aspect of the Present Invention)

The solidifying material according to the first aspect of the presentinvention is characterized in that the solidifying material is a blockcopolymer comprising, as segments A, a polymer non-compatible with thecell electrolyte solution and, as segments B, a polymer compatible withthe cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution; a smallest unit of the block copolymer is A-B-A;and to each of the segments B, at least one group selected from thegroup consisting of a carboxyl group, an ester group, a hydroxyl group,a sulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded via a —S— bond or a —C— bond.

The block copolymer employed as a raw material for the solidifyingmaterial is a block copolymer of segments A and segments B. Each segmentB contains an unsaturated double bond group. Such feed block copolymersare disclosed, for example, in Kogyo Zairyo (Industrial Materials),“Tokushu—Netsukasosei Elastomers (Special Edition—ThermoplasticElastomers”, 24(12) 1976 and Sekiyu Gakkai Shi (Bulletin of the JapanPetroleum Institute), 18, 565 (1975). These block copolymers are highmolecular substances each of which has a structure such as (SegmentA)-(Segment B)-(Segment A) that the segment B, which has an unsaturateddouble bond, is flanked at two points thereof between the segments A, asexpressed under the name of the so-called tele-block copolymer type,multi-block copolymer type or star-shaped block copolymer type. Further,a single-block copolymer composed of segments A and segments B may alsobe mixed in these high molecular substances. Preferably, each of thesehigh molecular substances has a weight average molecular weight of from10,000 to 500,000.

As the segments A which constitute the solidifying material according tothe first aspect of the present invention, a polymer selected frompolystyrene, polyethylene or polypropylene is preferred. As the segmentsB, on the other hand, a polymer selected from polybutadiene,polychloroprene or polyisoprene is preferred. The segments A are in acrystallized form in the block copolymer, and keep the block copolymerphysically crosslinked at room temperature. Further, these segments Ahave high non-compatibility (insolubility) with a cell electrolytesolution, for example, a thick aqueous solution of potassium hydroxide.

The content of the segments A in the block copolymer can preferably bein a range of from 0.5 to 70 wt. %. A content lower than 0.5 wt. % istoo low to exhibit the crystallization effect of the segments A for thecopolymer. A content higher than 70 wt. %, on the other hand, results ina solidifying material having a smaller liquid absorption rate for theelectrolyte solution. The preferred content is in a range of from 1.0 to50 wt. %.

The segments B which also constitute the solidifying material accordingto the first aspect of the present invention is a polymer selected fromthe group consisting of polybutadiene, polychloroprene and polyisoprene,and the polymer can preferably have a weight average molecular weight offrom 10,000 to 300,000. The content of the segments B in the blockcopolymer may be 99.0 to 50 wt. %, preferably 95.5 to 30 wt. %.

Each segment B has a group, which is compatible with the electrolytesolution, via a —S— bond or a —C— bond. Examples of the compatible groupcan include a carboxyl group, ester groups, a hydroxyl group, a sulfonicgroup, an amino group, cyclic carbonate groups, and ether groups.Illustrative of the ether groups are homopolymers and block or randomcopolymers of polyoxyethylene groups or polyoxypropylene groups. Theester group, through its hydrolysis or the like, can make the segment Bexhibit compatibility with the electrolyte solution. These compatiblegroups should be suitably selected and combined depending upon theelectrolyte solution. For example, electrolyte solutions include bothaqueous and non-aqueous systems. It is preferred to select suchcompatible groups as permitting absorption of a solution of one of thesesystems and to introduce them into the segments B.

As an illustrative method for the introduction of the above-describedcompatible groups into the segments B, a compatible compound containingone mercapto group (—SH), acid sodium sulfite (sodium hydrogensulfite)or maleic anhydride is added to double bonds in the segments B. Examplesof the mercapto-containing compound can include thioglycolic acid,thiolactic acid, thiomalic acid, thiosuccinic acid, thiosalicylic acid,mercaptopropane-sulfonic acid, thioethanolamine, thioglycol, andthioglycerin. In the presence of a free radical generator, for example,azobisisobutyronitrile, azobiscyanovaleric acid, benzoyl peroxide,lauroyl peroxide, cumene hydroperoxide, ammonium persulfate or an alkalisalt thereof, or hydrogen peroxide, or by simply heating, the mercaptocompound, maleic anhydride or acid sodium sulfite is added to thesegments B to obtain the solidifying material according to the firstaspect of the present invention.

The introduction of polyethylene oxide groups or polypropylene oxidegroups into the segments B via —C— bonds or —S— bonds can be effected byintroducing hydroxyl groups or carboxyl groups into the copolymer inaccordance with the above-described method and thenaddition-polymerizing ethylene oxide or propylene oxide to the groups sointroduced. The polyethylene oxide groups or polypropylene groups soadded may preferably have a weight average molecular weight in a rangeof from 200 to 1,000.

Upon introduction of the compatible groups, it is preferred to conductthe introduction by using a solvent. Preferred examples of the solventcan include cyclohexane, methylcyclohexane, toluene, xylol, terpene,pentane, naphthene, kerosene, methyl ethyl ketone, acetone,tetrahydrofuran, dimethylformaldehyde, dioxolane, dioxane,ethylcellosolve, diethylcellosolve, ethyl acetate, propyl acetate, butylacetate, butyl alcohol, propyl alcohol, isopropyl alcohol, ethylalcohol, methanol, and water.

The solidifying material according to the first aspect of the presentinvention obtained as described above can take any form, including aform in which the solidifying material is dissolved in an aqueoussystem, including a form in which the solidifying material is dispersedin water, a form in which the solidifying material is dispersed in asolvent, a form in which the solidifying material is dissolved in asolvent, and a powdery form. The production process itself of thesolidifying material obtained as described above is disclosed in JP1-168968 A in the name of Dainichiseika Color & Chemicals Mfg. Co., Ltd.

(Second Aspect of the Present Invention)

The solidifying material according to the second aspect of the presentinvention is characterized in that the solidifying material is a graftcopolymer comprising, as segments A, a polymer non-compatible with thecell electrolyte solution and, as segments B, a polymer compatible withthe cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution; and to each of the segments B, at least one groupselected from the group consisting of a carboxyl group, an ester group,a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonategroup and a polyoxyalkylene group is bonded.

Illustrative of the segments A are polystyrene, polyethylene,polypropylene, poly(meth)acrylate esters and polyacrylonitrile, each ofwhich has a weight average molecular weight of form 3,000 to 20,000 andcontains an α,β-ethylenically unsaturated group at an end thereof. Aweight average molecular weight lower than 3,000 is too low to make thesegments A exhibit their crystallization-dependent, physicalcrosslinking effect in the graft copolymer. A weight average molecularweight higher than 20,000, on the other hand, makes it difficult toproduct the graft copolymer. The content of the segments A maypreferably be in a range of from 1 to 70 wt. %. A content lower than 1wt. % cannot exhibit the crosslinking effect of the segments A throughcrystallization, while a content higher than 70 wt. % leads to asolidifying material having a small absorption for an electrolytesolution. Contents outside the above range are not preferredaccordingly. More preferably, the content is in a range of form 2.5 to50 wt. %.

Examples of a monomer, which has a group compatible with the electrolytesolution and is to be graft-copolymerized with the segments A, caninclude (meth) acrylic acid, maleic acid, vinylbenzoic acid,(meta)styrenesulfonic acid, 2-acryloylamido-2-methyl-1-propanesulfonicacid, methacryloxypropylsulfonic acid, vinylsulfonic acid, alkali metalsalts such as polyoxyethylene alkyl ether sulfosuccinic acid or alkalinemetal salts thereof, 4-vinylpyridine, 2-vinylpyridine,dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate,(2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, and 2-hydroxypropyl (meth)acrylate.

From these monomers, a preferred monomer is selected depending upon theelectrolyte solution. Electrolyte solutions include both aqueous andnon-aqueous systems. It is preferred to graft-polymerize such a monomeras permitting absorption of a solution of one of these systems. Two ormore of the monomers may be graft-copolymerized as needed.

When the solidifying material according to the second aspect of thepresent invention is used for a non-aqueous electrolyte solutionrepresented by an electrolyte solution for lithium cells, a monomerusable for the production of the segments B is a monomeric ester havinga general polymerizable unsaturated group. Illustrative of such amonomeric ester are methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, lauroyl(meth)acrylate, stearyl (meth)acrylate, acrylonitrile, styrene, vinylacetate, (2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, (meth)acryloyl-containing polyethylene glycol (weight average molecularweight: 200 to 1,000), (meth)acryloyl-containing polypropylene glycol(weight average molecular weight: 200 to 1,000), and(meth)acryloyl-containing polyethylene glycol/polypropylene glycolcopolymer (weight average molecular weight: 200 to 1,000).

Among these, monomers important for the formation of segments B, whichare suited for the transfer of ions in a non-aqueous electrolyteemployed in cells, are monomers containing polyoxyalkylene groups whichinclude at least a polyethylene glycol group. Use of a monomer, whichcontains a polyethylene glycol group as is or contains a copolymer ofethylene oxide and propylene oxide, is preferred.

To enhance the insolubility of the solidifying material according to thesecond aspect of the present invention in the electrolyte solution, apolyfunctional monomer may also be copolymerized in a small proportionupon conducting the graft copolymerization. Examples of such apolyfunctional monomer can include aromatic divinyl compounds such asdivinylbenzene and divinylnaphthalene; and (meth)acrylates such aspolyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,tripropylene glycol di(meth)acrylate, hydroxypivalate ester neopentylglycol di(meth)acrylate, trimethylol propane tri(meth)acrylate,pentaerythritol tri (meth) acrylate, and dipentaerythritol hexa(meth)acrylate. These polyfunctional monomers can be added preferably in aproportion of 5 wt. % or less of the above-mentioned monofunctionalmonomer.

As a polymerization initiator usable upon graft copolymerization, thesame polymerization initiator as that described above in connection withthe first aspect of the present invention can also be used. Further, asa solvent usable upon graft copolymerization, the same solvent as thatdescribed above in connection with the first aspect of the presentinvention can also be used.

The solidifying material according to the second aspect of the presentinvention obtained as described above can take any form, including aform in which the solidifying material is dissolved in an aqueoussystem, including a form in which the solidifying material is dispersedin water, a form in which the solidifying material is dispersed in asolvent, a form in which the solidifying material is dissolved in asolvent, and a powdery form. The production process itself of thesolidifying material obtained as described above is disclosed in JP2-1715 A and JP 2-265909 in the name of Dainichiseika Color & ChemicalsMfg. Co., Ltd.

The solidifying material according to each of the first and secondaspects of the present invention may preferably be in the form of afilm. Examples of a film-forming process can include the casting processin which a solution or dispersion of the solidifying material is castand dried, the extrusion process in which the solidifying material in apowdery form is dispersed in a thermoplastic resin and the resultingdispersion is extruded, and a process in which such a dispersion isformed into a film by calendering. Especially in order to impartexcellent strength to a film to be obtained, a natural or syntheticresin insoluble in the electrolyte can be added to the solution orpowder of the solidifying material.

Illustrative of the natural or synthetic resin are natural rubber, andsynthetic rubbers such as chloroprene, isoprene, butyl rubber,styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, andhydrogenation products thereof. These copolymers can each be of any oneof bonding types of random bonding, block bonding and graft bonding. Thecontent of the natural or synthetic resin is preferably 85 wt. % or lessbased on the solidifying material. A content higher than 85 wt. %results in a film-shaped solidifying material, the electricalconductivity of which is too low to use it as a solidifying material. Asa still further additive, a plasticizer can also be used. Especially,process oil having chemical resistance is effective.

The thickness of each film obtained as described above is 0.0001 to 2mm. A thickness smaller than 0.0001 mm involves a potential problem inthat a homogeneous film may not be obtained. A thickness greater than 2mm, on the other hand, makes it difficult to form the solidifyingmaterial into a film and, even if such a film is obtained, a long timeis needed for the absorption of the electrolyte. Moreover, such a greatthickness cannot provide a thin cell.

(Third Aspect of the Present Invention)

The solidifying material according to the third aspect of the presentinvention is characterized in that the solidifying material comprises afilm or sheet of a polymer having properties the that polymer isinsoluble in the cell electrolyte solution but the polymer absorbs andsolidifies the cell electrolyte solution, and a backing reinforcing thefilm or sheet; and the backing is a woven fabric, a nonwoven fabric or aporous film. Preferred examples of the above-described solidifyingmaterial can be the block copolymer in the first aspect of the presentinvention and the graft copolymer in the second aspect of the presentinvention. Other polymers can also be used.

Illustrative of such other polymers are those obtained by crosslinkinghydrophilic polymers (i.e., so-called superabsorbent polymers). As thesesuperabsorbent polymers, conventionally known superabsorbents are allusable, and no particular limitation is imposed thereon. Illustrativeare starch-based graft copolymers such as a hydrolysis product ofstarch-acrylonitrile graft copolymer, starch-acrylic acid graftcopolymer, starch-styrenesulfonic acid graft copolymer,starch-vinylsulfonic acid graft copolymer, and starch-acrylamidecopolymer; cellulose derivatives such as cellulose-acrylonitrile graftcopolymer, cellulose-styrene-sulfonic acid graft copolymer, and acrosslinked product of carboxymethylcellulose; hyaluronic acid, agarose,and collagen; polyvinyl alcohol derivatives, such as crosslinkedpolyvinyl alcohol polymer and polyvinyl alcohol supersorbentgel/elastomer; crosslinked polyacrylic acid polymer, sodiumacrylate-vinyl alcohol copolymer, saponified product ofpolyacrylonitrile polymer, hydroxyethyl methacrylate polymer, maleicanhydride (co)polymers, vinylpyrrolidone (co)polymers, crosslinkedpolyethylene glycol-diacrylate polymer, crosslinked polypropyleneglycol-diacrylate polymer, ester-base polymers, amide-based polymers,poly[(2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate],poly(N,N′-dimethyl-acrylamide), poly (N-vinylacetamide); and crosslinkedproducts thereof. These supersorbent polymers can absorb electrolytesolutions. Each of these superabsorbent polymers can be fixed on abacking, which will be described subsequently herein, by using adispersion in which the polymer has been dispersed with an appropriatedispersant in a non-aqueous medium.

In cadmium-nickel cells or nickel-hydrogen secondary cells,uncrosslinked copolymers each of which has been obtained using acrylicacid (or an acrylate salt), acrylamide or the like as a principalcomponent and has a weight average molecular weight of from 50,000 to1,000,000 can be used in place of the above-described (cc)polymers.

In lithium cells as typical examples of those making use of non-aqueouselectrolyte solutions, polymers obtained by copolymerizing monomericesters or the like to the above-described polymers can be used. Examplesof such monomeric esters can include methyl (meth) acrylate, ethyl(meth) acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate,tert-butyl (meth)acrylate, lauroyl (meth)acrylate, stearyl(meth)acrylate, acrylonitrile, styrene, and vinyl acetate. To strengthenthe solidifying material which has swollen as a result of absorption ofthe electrolyte solution, the above-described polyfunctional monomer maybe copolymerized in a small proportion to crosslink the solidifyingmaterial.

As a polymerization catalyst, conventionally known radicalpolymerization initiators are all usable, and no limitation is imposedon the polymerization catalyst. Illustrative are azobisisobutyronitrile,azobiscyanovaleric acid, benzoyl peroxide, lauroyl peroxide,cumenehydroperoxide, ammonium persulfate and alkali salts thereof, andhydrogen peroxide. It is also possible to conduct the polymerization inthe presence or absence of such a polymerization catalyst, underirradiation of ultraviolet rays, electron beams or radiation, or underheat.

When the electrolyte is an aqueous solution, the solidifying materialmay preferably contain ion-compatible groups. When the electrolyte is anon-aqueous solution, it is important for the solidifying material tocontain polyethylene oxide groups which take part in the transfer ofalkali ions. The amount of the electrolyte to be absorbed in thesolidifying material can be in a range of from 5 to 5,000 wt. % based onthe solidifying material. An absorption smaller than 5 wt. % cannotprovide the solidified electrolyte solution with sufficient electricalconductivity, while an absorption greater than 1,000 wt. % results inswollen gel (the solidifying material in a swollen form as a result ofabsorption of the electrolyte solution) of considerably reducedstrength.

Among the above-described solidifying materials, the solidifyingmaterial according to the third aspect of the present invention isgenerally used after mechanically grinding it to a particle size of 100μm or smaller, preferably 50 μm or smaller. Inclusion of particlesgreater than 100 μm makes it difficult to form a thin, film-shapedsolidifying material. On the other hand, the solidifying materialsaccording to the first and second aspects of the present invention, eachof which contains the segments A, feature good dispersibility in otherpolymers having no compatibility with the electrolyte solution, andtheir particle sizes can be easily reduced to several 100 nm to 10 μm.

The solidifying material according to the third aspect of the presentinvention is composed of the above-described solidifying material andthe reinforcing backing. To improve the formability of the solidifyingmaterial and the strength of the thus-formed product, it is preferred toadd, to the solidifying material, a polymer having elastomeric propertybut no compatibility with the electrolyte solution. Such a polymer canbe any one of the natural and synthetic rubbers described above inconnection with the first and second aspects of the present invention.

To reinforce the solidifying material, a woven fabric, a nonwoven fabricor a porous film can be used as a backing. The materials of thesebackings are, for example, polyethylene, polypropylene, polyamides,polyacrylonitrile, polyesters, polyvinyl chloride, and polyvinylfluoride. Polyethylene, polypropylene and polyacrylonitrile arepreferred for their excellent chemical resistance. In the case of anaqueous electrolyte solution, use of a hydrophilic backing with sulfonicgroups or the like introduced therein is preferred in order to stabilizea coating formulation containing the solidifying material. Alsopreferred is a backing obtained by hydrolyzing a woven fabric ornonwoven fabric of polyacrylonitrile fibers at surfaces thereof withconcentrated sulfuric acid or the like to introduce carboxyl groupstherein. It is sufficient to apply such treatment only to fibersurfaces.

The woven fabric, nonwoven fabric or porous film as the backing maypreferably have a thickness in a range of from 1 to 1,200 μm, morepreferably from 2 to 400 μm. A thickness smaller than 1 μm makes itdifficult to produce such a woven fabric, nonwoven fabric or porousfilm, while a thickness greater than 1,200 μm makes it difficult to forma thin, film-shaped solidifying material. The opening percentage of thenonwoven fabric Lay preferably in a range of from 95 to 10%. An openingpercentage higher than 95% bring about only small reinforcing effect forthe solidifying material, while an opening percentage lower than 10%leads to a film of extremely low electrical conductivity afterabsorption and solidification of the electrolyte. No particularlimitation is imposed on the type of weave of the woven fabric, andexamples of the weave can include plain weave, twilled weave, plaindutch weave and twilled dutch weave.

As a process for fixing the solidifying material on the reinforcingbacking, (1) the reinforcing backing is dipped in a coating formulation(a dispersion of the solidifying material), is squeezed through a mangleor the like, and is then dried, (2) the coating formulation is coatedonto the reinforcing backing by a gravure coater, a comma (knife)coater, a reverse coater or a blade coater, and is then dried, (3) thesolidifying material is formed into a film in a manner by a knownmethod, and the film is then bonded onto the reinforcing backing (forexample, a cast film of the solidifying material is bonded underpressure through heated rolls or on a press. In some instances, thecoating formulation can be fixed on the reinforcing backing by coatingthe coating formulation onto the reinforcing backing, immersing thethus-coated reinforcing backing in a poor solvent to make the layer ofthe solidifying material porous, and then drying the reinforcing backingwith the resultant porous layer carried thereon.

No particular limitation is imposed on a process for having theelectrolyte solution absorbed in the solidifying material according tothe present invention. For example, it is possible to have theelectrolyte solution absorbed in the solidifying material in the form ofa film reinforced with the reinforcing backing. As an alternative, it isalso possible to add the electrolyte solution to a solution of thesolidifying material and, subsequent to having the resultant solutionabsorbed in the reinforcing backing in the form of a film reinforcedwith the reinforcing backing, to conduct drying to obtain thesolidifying material in the form of the film with the electrolytesolution absorbed therein. In some instances, it is also possible tohave the electrolyte solution absorbed in the solidifying material bybonding a backing on each electrode of a cell, dipping the electrode ina solution of the solidifying material with the backing bonded on theelectrode or coating the solution onto the backing on the electrode, andthen conducting drying. This process is effective for improving themutual contact between the electrode and the film, which has been formedby solidifying the electrolyte solution, at the interface therebetween.

Examples of a cell electrolyte to be absorbed in the above-describedsolidifying materials according to the first to third aspects of thepresent invention can include dilute sulfuric acid, potassium chloride,zinc chloride, potassium hydroxide, and lithium salts such as lithiumperchlorate, LiBF, LiPF₆, LiCF₃SO₃, LiN(CF₃SO₂)₂ and LiC(CF₃SO₂)₂.

Illustrative of a medium in the above-described electrolyte solution arewater, ethylene carbonate, propylene carbonate, dimethyl carbonate,ethyl methyl carbonate, dimethyl carbonate, γ-butyrolactone, methylformate. methyl acetate, dimethyl sulfoxide, acetonitrile,N-methyl-pyrrolidone, tetrahydrofuran, diethylene glycol dimethyl ether,diethyl ether, 1,2-dimethoxyethane, and mixtures thereof.

The present invention will next be described more specifically based onExamples and Referential Examples, in which designations of “part” or“parts” and “%” are each on a weight basis unless otherwise specificallyindicated.

(First Aspect of the Present Invention)

EXAMPLE 1 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL A)

A block copolymer (15 parts) composed of polystyrene, polybutadiene andpolystyrene (polystyrene content: 30%, weight average molecular weight:100,000) was dissolved in a mixed solvent formed of toluene (45 parts),cyclohexane (75 parts) and methyl ethyl ketone (35 parts), and theresulting solution was heated to 70° C. under a nitrogen gas stream.Into the solution, thioglycolic acid (20 parts) andazobisisobutyronitrile (0.3 part) were added, followed by an additionreaction for 12hours. The reaction mixture was washed with a saturatedaqueous solution of Na₂SO₄ to extract off unreacted thioglycolic acidfrom the reaction mixture. A 15% solution of potassium hydroxide inmethanol was added to the thus-washed solution to convert carboxylgroups in the resultant solidifying material into potassium salts.

The solvent was then distilled off to adjust the solid content of thesolution to 30%. As a result of an analysis of the solid matter in thesolution by infrared absorption spectroscopy, the unsaturated groups ofthe polybutadiene were confirmed to be substantially eliminated. Theparticle size of particles suspended in the solution was measured by thelight scattering method (Coulter A4 particle sizer). As a result, theparticles were found to have a particle size of about 100 nm. Further,the solidifying material A taken out of the solution had a swellingindex of 3,000% in deionized water.

Test 1 (Hot Potassium Hydroxide Durability Test)

The above-described solidifying material A was placed in a 20% aqueoussolution of potassium hydroxide (electrolyte solution) and wascontinuously left over at 80° C. for 3 months. The absorption of thepotassium hydroxide solution in the solidifying material A was 400%, andno changes were observed on the solidifying material A.

Test 2

The above-prepared solution of the solidifying material A, the solidcontent of which was 30%, and a solution (solid concentration: 20%) of apolystyrene-polybutadiene-polystyrene (SBR-TR) block copolymer(polystyrene content: 30%, weight average molecular weight: 100,000) intoluene/methyl ethyl ketone were mixed at the respective solid ratios(weight ratios) described in Table 1. The resultant liquid mixtures werecast and dried on glass plates to form films of about 100 μm inthickness, respectively.

In Table 1, liquid absorption rates of each film are shown together withthe corresponding electrical conductivity data of the film in forms withliquids absorbed therein. The liquid absorption rates were determined aswill be described next. Samples of the film were immersed in solutions(deionized water, and a 10% aqueous solution of potassium chloride),respectively. From weight changes of the film samples after theimmersion, the liquid absorption rates were calculated. On the otherhand, the electrical conductivities were determined as will be describednext. Samples of the film were immersed at 25° C. for 24 hours in the 3months in the solutions (the deionized water, and the 10% aqueoussolution of potassium chloride), respectively. The film samples weretaken out of the solutions, and were sandwiched between platinum platesof 1 cm². Across the respective film samples, voltages of 6V wereapplied, respectively. From the resulting currents, the electricalconductivities were calculated.

TABLE 1 Electrical Electrical conductivity Absorption conductivity offilm with Absorption rate of Solidifying Electrical of film with aqueousrate of aqueous material A/ conductivity deionized solution of deionizedsolution SBR-TR of dry film water absorbed KCl absorbed water of KCl(weight ratio) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (wt. %) (wt. %)  0/100 0 00 0 0 25/75  1.2 × 10⁻⁷  5.7 × 10⁻³ 5.8 × 10⁻³ 250 150 50/50 2.45 × 10⁻⁶1.29 × 10⁻³ 6.9 × 10⁻³ 450 200 75/25 6.94 × 10⁻⁵ 2.42 × 10⁻³ 4.36 ×10⁻²  700 250 100/0   7.8 × 10⁻⁴  5.1 × 10⁻² 7.7 × 10⁻² 3,000 300

It has been found from Table 1 that, when the content of the solidifyingmaterial A is 25% or higher, films with the respective solutionsabsorbed therein show sufficient electrical conductivities. From theseresults, it is understood that the solidifying material according to thepresent invention is useful as a solidifying material for electrolytesolutions in “CADNICA” cells (Ni—Cd cells) or nickel-hydrogen cells.

EXAMPLE 2 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL B)

A block copolymer (8 parts) composed ofpolystyrene—polybutadiene—polystyrene (polystyrene content: 30%, weightaverage molecular weight: 100,000) was dissolved in a mixed solventformed of a petroleum-base solvent (50 parts) and methyl ethyl ketone(80 parts), and the resulting solution was heated to 70° C. under anitrogen gas stream. Into the solution, thioglycerin (12 parts) andazobisisobutyronitrile (0.2 part) were added, followed by an additionreaction for 12 hours. After completion of the reaction, the reactionmixture was washed with a saturated aqueous solution of Na₂SO₄ toextract off unreacted thioglycerin from the reaction mixture.

Ethylene oxide was blown into the solution in the presence of an alkalicatalyst to have 3 moles of ethylene oxide added per hydroxyl group. Theparticle size of fine particles in the solution was measured by thelight scattering method (Coulter N4 particle sizer). As a result, theparticle size was found to be about 200 nm. The swelling index of asolidifying material B, which had been taken out of the solution, indeionized water was 2,000%.

Incidentally, the solidifying material B can also absorb other solventssuch as tetrahydrofuran, dimethylformamide and methyl ethyl ketone toabout 500 to 1,000%. Therefore, the solidifying material B can also beused as a solidifying material for lithium cell electrolyte solutionscontaining aprotic solvents.

(Second Aspect of the Present Invention)

EXAMPLE 3 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL C)

Acrylic acid (30 parts), polyethylene glycol monomethacrylate (70 parts,weight average molecular weight: about 300) and methacryloyl-containingpolystyrene (30 parts, weight average molecular weight: about 6,000)were dissolved in a mixed solvent formed of methyl ethyl ketone (100parts) and cyclohexane (180 parts). Azoisobutyronitrile (1.1 parts) wasmixed with the solution, followed by polymerization at 70° C. for 8hours under a nitrogen gas stream. After cooling, the carboxyl groups inthe resulting solidifying material C were neutralized with a 15%solution of caustic potash in methanol. The solvent was distilled off toadjust the solid content to 50%. The particle size of the solidifyingmaterial C in the solution was about 300 nm. The absorption rate of thesolidifying material C, which had been taken out of the solution, indeionized water was about 2,000% based on its weight.

Test 3

The above-prepared solution of the solidifying material C and a solution(solid concentration: 20%) of a polystyrene-polybutadiene-polystyrene(SBR-TR) block copolymer (polystyrene content: 30%, weight averagemolecular weight: 100,000) in toluene/methyl ethyl ketone were mixed atthe respective weight ratios (solid ratios) described in Table 2. Theresultant liquid mixtures were formed by casting into films of about 100μm in thickness, respectively. Measurements of their liquid absorptionrates and electrical conductivities were conducted by the same methodsas in Test 1.

TABLE 2 Electrical Electrical conductivity Absorption conductivity offilm with Absorption rate of Solidifying Electrical of film with aqueousrate of aqueous material C/ conductivity deionized solution of deionizedsolution SBR-TR of dry film water absorbed KCl absorbed water of KCl(weight ratio) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (wt. %) (wt. %)  0/100 0 00 0 0 25/75  1.2 × 10⁻¹¹ 1.1 × 10⁻³ 2.8 × 10⁻³ 250 160 50/50 1.0 × 10⁻⁶1.1 × 10⁻² 1.4 × 10⁻² 350 200 75/25 2.9 × 10⁻⁶ 2.2 × 10⁻² 8.4 × 10⁻² 510220

It has been found from Table 2 that films, each of which contains thesolidifying material of the present invention at 25% or more andcontains an electrolyte solution absorbed therein, show sufficientelectrical conductivities. From these results, it is understood that thesolidifying material according to the present invention is useful as asolidifying material for electrolyte solutions in “CADNICA” cells (Ni—Cdcells) or nickel-hydrogen cells. Further, the solidifying materialaccording to the present invention can also absorb solvents other thanwater, such as tetrahydrofuran, dimethylforamide and methyl ethylketone, at rates of from about 300 to 800%. Therefore, the solidifyingmaterial according to the present invention can also be used as asolidifying material for lithium cell electrolyte solutions containingaprotic solvents.

(Third Aspect of the Present Invention)

EXAMPLE 4 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL D)

Following the process disclosed in JP 55-56615 A, potassiumthioglycolate was added to 95 mole % of the double bonds ofpolybutadiene in a block copolymer composed ofpolystyrene-polybutadiene-polystyrene (polystyrene content: 40%, weightaverage molecular weight: 150,000) to produce a solidifying material D.

A mixed solution of toluene/cyclohexane/MEK (35/35/30, weight ratio) andthe solidifying material D were mixed to adjust the solid content to25%. The average dispersed particle size of the solidifying material Din the solution was measured by the light scattering method (Coulter A4particle sizer) (this will apply equally hereinafter). As a result, theaverage dispersed particle size was found to be about 100 nm. Theswelling index of the solidifying material D in deionized water was100-fold.

EXAMPLE 5 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL E)

In a similar manner as described above, thioglycol was added to 90 mole% of the double bonds of polybutadiene in a block copolymerpolystyrene-polybutadiene-polystyrene (polystyrene content: 30%, weightaverage molecular weight: 100,000), and ethylene oxide (7 moles onaverage) was added to the hydroxyl groups of the thioglycol to produce asolidifying material E. The solidifying material E was mixed with amixed solvent of toluene/cyclohexanone/MEK (35/35/30, weight ratio) toadjust the solid content to 20%. The average dispersed particle size ofthe solidifying material E in the solution was about 100 nm. Theswelling index of the solidifying material E in deionized water was10-fold.

EXAMPLE 6 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL F)

A solidifying material F composed of potassium acrylate, polyethyleneglycol monomethacrylate (molecular weight: about 300) andmethacryloyl-containing polystyrene (molecular weight: about 6,000)[weight ratio: 70/30/20%] was mixed with a mixed solvent of methyl ethylketone/cyclohexane (60/40, weight ratio) to adjust the solid content to50%. The average dispersed particle size of the solidifying material Fin the solution was about 300 nm. The swelling index of the solidifyingmaterial F in deionized water was 30-fold.

EXAMPLE 7 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL G)

A crosslinked polymer composed of potassiumacrylate/N,N′-methylenebisacrylamide (99.5/0.5%) was produced as asolidifying material G by radical polymerization. The content ofwater-soluble components in the solidifying material G was 20%. Theswelling index of the solidifying material G in deionized water was200-fold.

EXAMPLE 8 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL H)

A commercial, crosslinked isobutylene/potassium maleate copolymer(isobutylene/potassium maleate=1/1, molar ratio) was provided as asolidifying material H. The swelling index of the solidifying material Hin deionized water was 320-fold.

EXAMPLE 9 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL I)

Crosslinked poly(N-vinylacetamide) obtained by radical polymerizationwas provided as a solidifying material I. The swelling index of thesolidifying material I in deionized water was 25-fold.

EXAMPLE 10 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL J)

Poly(sodium acrylate) produced by reverse-phase polymerization andhaving an average particle size of 200 μm was provided as a solidifyingmaterial J. The swelling index of the solidifying material J indeionized water was 1,000-fold.

EXAMPLE 11 (PRODUCTION EXAMPLE OF A SOLIDIFYING MATERIAL K)

An acrylic acid (89.1%)/styrene (10%)/divinylbenzene (0.9%, purity: 55%)copolymer, which had been obtained by bulk polymerization in thepresence of azobutyronitrile as a polymerization initiator, wasneutralized with potassium hydroxide, dried, and then ground. Fineparticles of from 1 to 5 μm in particle size were provided as asolidifying material K. The swelling index of the solidifying material Kin deionized water was 130-fold.

The following reinforcing backings were provided:

(1) Woven fabric obtained by sulfonating the surfaces of a polypropylenefabric (thickness: 0.122 mm, basis weight: 33 g/m², thread thickness:0.080 mm, opening diameter: 0.098 mm).

(2) Nonwoven fabric (A) obtained by treating a nonwovenpolyacrylonitrile fabric (thickness: 0.081 mm, basis weight: 45 g/m²)with sulfuric acid to hydrolyze fibers at the surfaces thereof andforming potassium salts.

(3) Nonwoven fabric (B) obtained by sulfonating a nonwoven fabric(polypropylene fibers, thickness: 0.1 mm, basis weight: 33 g/m², airresistance: 3 sec/L) at surfaces thereof.

EXAMPLE 12 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 1)

The solidifying material D, a polystyrene-polybutadiene block copolymer(styrene content: 30%, weight average molecular weight: 100,000; thesewill apply equally hereinafter) and an aromatic process oil were mixedat a weight ratio of 64/21/15 with toluene to adjust the solid contentto 20%. A coating formulation of the solidifying material was obtainedaccordingly. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 1 of 0.11 mm in thickness (coat weight: 100 g/m² weightbasis; this will apply equally hereinafter).

EXAMPLE 13 (PRODUCTION EXAMPLE OF A SOLIDIGYING FILM 2)

The solidifying material F and the polystyrene-polybutadiene blockcopolymer were mixed at a weight ratio of 75/25 with toluene to adjustthe solid content to 20%. A coating formulation was obtainedaccordingly. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 2 of 0.15 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 14 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 3)

The solidifying material G and the polystyrene-polybutadiene blockcopolymer were mixed at a weight ratio of 70/30 with toluene to adjustthe solid content to 20%. A coating formulation was obtainedaccordingly. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 3 of 0.2 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 15 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 4)

The solidifying material G and the polystyrene-polybutadiene blockcopolymer were dispersed at a weight ratio of 70/30 in toluene by a“Dynomil” (high-speed bead mill) to adjust the solid content to 20%. Acoating formulation was obtained accordingly. The average dispersedparticle size of the solidifying material in the coating formulation wasabout 30 μm. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 4 of 0.2 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 16 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 5)

The solidifying material H and the polystyrene-polybutadiene blockcopolymer were dispersed at a weight ratio of 70/30 in tetrahydrofuranby a “Dynomill” (high-speed bead mill) to adjust the solid content to30%. A coating formulation was obtained accordingly. The averagedispersed particle size of the solidifying material in the coatingformulation was about 25 μm. The coating formulation was applied ontoboth sides of the woven fabric (1), and then dried at 80° C. for 24hours to obtain a solidifying film 5of 0.12 mm in thickness (coatweight: 100 g/m²).

EXAMPLE 17 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 6)

The solidifying material I and the polystyrene-polybutadiene blockcopolymer were dispersed at a weight ratio of 90/10 in tetrahydrofuranby a “Dynomill” (high-speed bead mill) to adjust the solid content to30%. A coating formulation was obtained accordingly. The averagedispersed particle size of the solidifying material in the coatingformulation was about 35 μm. The coating formulation was applied ontoboth sides of the woven fabric (1), and then dried at 80° C. for 24hours to obtain a solidifying film 6 of 0.12 mm in thickness (coatweight: 100 g/m²)

EXAMPLE 18 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 7)

The solidifying material D, the polystyrene-polybutadiene blockcopolymer and an aromatic process oil were mixed at a weight ratio of64/21/15 with toluene to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (A), and then dried at 80°C. for 24 hours to obtain a solidifying film 7 of 0.9 mm in thickness(coat weight: 40 g/m²).

EXAMPLE 19 (PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 8)

The solidifying material D, the polystyrene-polybutadiene blockcopolymer and an aromatic process oil were mixed at a weight ratio of64/21/15 with toluene to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (B), and then dried at 80°C. for 24 hours to obtain a solidifying film 8 of 0.12 mm in thickness(coat weight: 45 g/m²)

EXAMPLE 20 PRODUCTION EXAMPLE OF A SOLIDIFYING FILM 9)

A solidifying film 9 (coat weight: 10 g/m²) was obtained in an similarmanner as in Example 16 except that the nonwoven fabric (B) and thesolidifying material K were used instead of the woven fabric (1) and thesolidifying material H, respectively.

Referential Example 1 (Production Example of a Solidifying Film 10)

A cast film (solidifying film) 10 of 100 μm in thickness without thewoven fabric in Example 12 was produced.

Referential Example 2 (Production Example of a Solidifying Film 11)Referential Example 2 (Production Example of a Solidifying Film 11)

The solidifying material J and the polystyrene-polybutadiene blockcopolymer were dispersed at a weight ratio of 70/30 in toluene by a“Dynomill” (high-speed bead mill) to adjust the solid content to 30%. Acoating formulation was obtained accordingly. The average dispersedparticle size of the solidifying material in the coating formulation wasabout 200 μm. The coating formulation was applied onto both sides of thewoven fabric (B), and then dried at 80° C. for 24 hours to obtain asolidifying film 11 (coat weight: 100 g/m², thickness: not accuratelymeasurable as the thickness was not even).

Test 4

The individual solidifying films of the above-described Examples andReferential Examples were ranked in the following properties. Theresults are shown in Table 3.

(1) Strength of Solidifying Film

Using each film of 15 mm in width, its tensile strength was measured ata tensile speed of 100 mm/min by a strength measuring machine(“Strograph EL”, trade name; manufactured by Toyo Seiki Seisaku-sho,Ltd.) under an environment of 20° C. and 60% RH. Each sample wasmeasured 10 times, and an average of the measurement results wasrecorded as measurement data.

(2) Electrical Conductivity

Samples of each film were immersed at 20° C. for 24 hours in a 10%aqueous solution of potassium chloride and deionized water,respectively, and were then taken out. The samples were each heldbetween two platinum plates of 1 cm². From currents produced uponapplication of voltages of 6V across the samples, respectively, theelectrical conductivities of the samples were calculated.

(3) Liquid Absorption Rate (%)

Each film was immersed at room temperature for 24 hours in a 10% aqueoussolution of potassium chloride, and was then taken out. After thesurfaces of the film were wiped, the weight of the film was determined.The liquid absorption rate (%) of the sample was calculated inaccordance with the following formula.

<When no backing was included>

Liquid absorption rate (%)=[(W ₁ −W ₀)/W _(0])×100

W₁: Weight of the film after liquid absorption (g/m²)

W₀: Weight of the film before liquid absorption (g/m²)

<When a Backing Was Included>

Liquid absorption rate (%) =[(W ₁ −W _(s) −W ₀)/(W ₀−W_(s))]×100

W₁: Weight of the film after liquid absorption (g/m²)

W₀: Weight of the film before liquid absorption (g/m²)

W_(s): Weight of the backing (g/m²)

(4) Surface Condition

Each coating formulation was applied onto a woven fabric or nonwovenfabric. The coated surface was visually observed. The surface conditionwas ranked in accordance with the following standards.

A: Extremely smooth and uniform.

B: Smooth and good uniformity.

C: Rugged, and coating was difficult.

TABLE 3 Film Electrical conductivity (Ω⁻¹m⁻¹) Liquid absorption rate (%)Surface strength KCl solution Water KCl solution Water condition Ex. 1278 40 × 10⁻⁴ 10 × 10⁻⁴ 230 4,000 A Ex. 13 80.5 33 × 10⁻⁴  7 × 10⁻⁴ 200800 A Ex. 14 101 80 × 10⁻⁴ 45 × 10⁻⁴ 400 10,000 B Ex. 15 92 72 × 10⁻⁴ 35× 10⁻⁴ 350 20,000 B Ex. 16 70 35 × 10⁻⁴ 20 × 10⁻⁴ 270 10,000 B Ex. 17 1548 × 10⁻⁴ 15 × 10⁻⁴ 300 1,500 A Ex. 18 25 20 × 10⁻⁴ 10 × 10⁻⁴ 150 1,000A Ex. 19 120 35 × 10⁻⁴  7 × 10⁻⁴ 200 3,000 A Ex. 20 80 75 × 10⁻⁴ 50 ×10⁻⁴ 1,500 7,500 A Ref. Ex. 1 2 57 × 10⁻⁴ 50 × 10⁻⁴ 200 3,500 A Ref. Ex.2 100 0.1 × 10⁻⁴  Measurement 350 10,000 C (substantial was scatteringof impossible measurement data) Unit of film strength: N/1.5 cm

EXAMPLE 21 (PRODUCTION EXAMPLE OF SOLIDIFYING FILM 12)

The solidifying material E, the polystyrene-polybutadiene blockcopolymer, lithium perchlorate, ethylene carbonate and propylenecarbonate were mixed at a weight ratio of 1/0.5/1/10/10 withtetrahydrofuran to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (A), and then dried at 60°C. for 48 hours to obtain a solidifying film 12 of 0.12 mm in thickness.The film 12 had an ion conductivity of 2.0×10⁻³ S/cm, and was by nomeans usable in a lithium cell.

What is claimed is:
 1. A solidifying material for a cell electrolytesolution, characterized in that said solidifying material is a blockcopolymer comprising, as segments A, a polymer non-compatible with saidcell electrolyte solution and, as segments B, a polymer compatible withsaid cell electrolyte solution, and absorbs and solidifies said cellelectrolyte solution; a smallest unit of said block copolymer is A-B-A;and to each of said segments B, at least one group selected from thegroup consisting of a carboxyl group, a hydroxyl group, a sulfonicgroup, an amino group and cyclic carbonate group is bonded via a —S—bond or a —C— bond.
 2. A solidifying material according to claim 1,wherein each of said segments A is a polymer selected from the groupconsisting of polystyrene, polyethylene and polypropylene and having aweight average molecular weight of from 10,000 to 500,000 and a contentof said segments A in said block copolymer is 0.5 to 70 wt. %; and eachof said segments B is a polymer selected from the group consisting ofpolybutadiene, polychloroprene and polyisoprene and having a weightaverage molecular weight of from 10,000 to 300,000.
 3. A cellcomprising, as a constituent element, a solidifying material accordingto claim
 2. 4. A solidifying material according to claim 1, furthercomprising not greater than 85 wt. %, based on said block copolymer, ofan elastomer non-compatible with said cell electrolyte solution.
 5. Acell comprising, as a constituent element, a solidifying materialaccording to claim
 4. 6. A solidifying material according to claim 1,which is in a form of a film or sheet of from 0.0001 to 2 mm inthickness.
 7. A cell comprising, as a constituent element, a solidifyingmaterial according to claim
 6. 8. A cell comprising, as a constituentelement, a solidifying material according to claim
 1. 9. A solidifyingmaterial for a cell electrolyte solution, characterized in that saidsolidifying material is a graft copolymer comprising, as segments A, apolymer non-compatible with said cell electrolyte solution and, assegments B, a polymer compatible with said cell electrolyte solution,and absorbs and solidifies said cell electrolyte solution; and to eachof said segments B, at least one group selected from the groupconsisting of a carboxyl group, a hydroxyl group, a sulfonic group, anamino group and a cyclic carbonate group is bonded.
 10. A solidifyingmaterial according to claim 9, wherein each of said segments A is apolymer selected from the group consisting of polystyrene, polyethylene,polypropylene, polyacrylonitrile and poly(meth)acrylate ester having aweight average molecular weight of from 3,000 to 20,000, and a contentof said segments A in said graft copolymer is 0.5 to 70 wt. %.
 11. Acell comprising, as a constituent element, a solidifying materialaccording to claim
 10. 12. A solidifying material according to claim 9,further comprising not greater than 85 wt. %, based on said graftcopolymer, of an elastomer non-compatible with said cell electrolytesolution.
 13. A cell comprising, as a constituent element, a solidifyingmaterial according to claim
 12. 14. A solidifying material according toclaim 9, which is in a form of a film or sheet of from 0.0005 to 2 mm inthickness.
 15. A cell comprising, as a constituent element, asolidifying material according to claim
 14. 16. A cell comprising, as aconstituent element, a solidifying material according to claim
 9. 17. Asolidifying material for a cell electrolyte solution, characterized inthat said solidifying material is a block copolymer comprising, assegments A, a polymer non-compatible with said cell electrolyte solutionand, as segments B, a polymer compatible with said cell electrolytesolution, and absorbs and solidifies said cell electrolyte solution; andsmallest unit of said block copolymer is A-B-A; and to each of saidsegments B, at least one group selected from the group consisting of acarboxyl group, an ester group, a hydroxyl group, a sulfonic group, anamino group, a cyclic carbonate group and a polyoxyalkylene group isbonded via a —S— bond.
 18. A solidifying material according to claim 17,wherein each of said segments A is a polymer selected from the groupconsisting of polystyrene, polyethylene and polypropylene and having aweight average molecular weight of from 10,000 to 500,000 and a contentof said segments A in said block copolymer is 0.5 to 70 wt. %; and eachof said segments B is a polymer selected from the group consisting ofpolybutadiene, polychloroprene and polyisoprene and having a weightaverage molecular weight of from 10,000 to 300,000.
 19. A cellcomprising as a constituent element, a solidifying material according toclaim
 18. 20. A solidifying material according to claim 17, furthercomprising not greater than 85 wt. %, based on said block copolymer, ofan elastomer non-compatible with said cell electrolyte solution.
 21. Acell comprising as a constituent element, a solidifying materialaccording to claim
 20. 22. A solidifying material according to claim 17,which is in a form of a film or sheet of from 0.0001 to 2 mm inthickness.
 23. A cell comprising, as a constituent element, asolidifying material according to claim 17.